Friday, March 22, 2013

During late Stone Age there were a significant number of people living into older adulthood

The New York Times reports: Who Lives Longest?

Artwork from the NY Times.
A Swedish baby born in 1800 had a life expectancy of just 32 years. We know this because Sweden was one of the first countries to keep extensive records of births and deaths and, by 1800, had a reliable national system that allowed this morbid statistic to be calculated. That baby’s life may sound nasty, brutish and short, especially for a nation advanced enough to keep such detailed records, but before you imagine 19th-century Swedish teenagers suffering the regret and ennui of midlife crises, consider this: that same year, a 20-year-old Swede could reasonably expect to live another 37 years.

Life expectancy is an average, and it fluctuates with age as the risks we face change throughout our lifetimes. Both those facts make it a frequently misunderstood statistic. High infant-mortality rates depress the figure substantially. This can lead contemporary observers to the false conclusion that most humans died quite young, even in the not-so-distant past. (Were you ever told, as a petulant teenager, that you’d have been considered middle-aged in medieval Europe?)

“ ‘Life expectancy’ is this term that entered public lingo without public understanding of what it really means,” says Andrew Noymer, associate professor of public health and sociology at the University of California, Irvine. Our hypothetical Swedish baby’s 1832 expiration date is, of course, nothing of the sort. It’s a way of expressing, statistically, that lots of babies and small children were dying in 19th-century Sweden. By simply surviving childhood, a young Swede could expect a relatively long life — and if he was lucky, aproper midlife crisis.

But so could Fred Flintstone. In the last decade, scientists have concluded that humans have lived into older adulthood since 30,000 years ago, during the Upper Paleolithic (part of the era more commonly known as the Stone Age). Michael Gurven, a professor of anthropology at U.C. Santa Barbara who has studied modern hunter-gatherer and horticultural tribes, found that people in these societies who survived childhood lived about as long as 19th-century Swedes did — into their 50s and beyond. His work is one clue that suggests Enlightenment Age Europeans could have had the same longevity as our ancestors who painted caves and hunted the woolly mammoth.

Before the Upper Paleolithic, early humans really did die young, most before their 30th birthdays. Then, during the late Stone Age, there was a significant increase in the number of people living into older adulthood. The scientific and technological advances that made the modern era possible are well known to us, but the Upper Paleolithic was also host to a flourishing of early human culture.
Rachel Caspari, a paleoanthropologist at Central Michigan University, studies the life spans of ancient humans, their ancestors and close relatives — together, known as hominins. In 2004, she and a colleague examined teeth from 768 hominin fossils representing three million years of primate evolution.

Looking at wear and other signs of aging in the teeth, Caspari split the fossils into groups of old and young adults, creating rough approximations of ancient demographics. Examing a span from between 100,000 and 30,000 years ago, Caspari found about four old adults for every 10 young adults. But beginning around 30,000 years ago, during the Upper Paleolithic, this reversed: Caspari counted 20 old adults for every 10 young adults.

This demographic shift coincided with an explosion of cultural production: clay figurines; carvings made of bone, wood and stone; cave art and jewelry making; and complex burial practices. According to Caspari, it was longer human life spans that seem to have made this flourishing possible. Having more time on earth allows our species to progress.

Read the full story at The New York Times

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